I. Field of the Invention
The invention relates to a method and a device for managing the operation of a nitrogen oxide trap, and for diagnosing its aging condition for an engine operating with a lean mixture, that is under conditions of excess oxygen with regard to the fuel.
II. Description of Related Art
Patent application FR 2 843 044 already teaches a method and a device for managing the operation of a nitrogen oxide trap for such engines.
The method according to that document uses an on/off type oxygen probe to detect the end of the activity of reducing the nitrogen oxides adsorbed on a catalyst of the nitrogen oxide trap type. According to this method, the end of bleed is detected at a standard operating temperature of the gas sensor, between about 650° and 800° C.
In that document, the end of bleed is detected by the presence of a second jump in the electrical signal delivered by the oxygen probe, placed downstream of the trap. This second jump is used as an indicator of the end of bleed.
The easy detection of the second jump according to the method of said document has the drawback that it can unfortunately be disturbed by various parameters.
The first of them is associated with the more or less fully achieved control of the composition of the exhaust gases leaving the engine, thereby causing fluctuations in the signal from the probe, and consequently false detections of the end of bleed.
The second parameter is associated with the time for detecting the first plateau, which proves too short to be always reliable.
The final parameter is associated with the need to have a sufficient probe signal amplitude for correctly detecting the second jump on the curve.
Finally, this prior method has the drawback of not allowing a diagnosis of the aging condition of a nitrogen oxide trap during its use.
The need therefore remains to have a method for managing the operation of a nitrogen oxide trap, while being able to diagnose its aging condition, and hence its operating condition for an internal combustion engine running on a lean mixture.